This invention relates to electrochemical cells. More particularly, it is concerned with primary electrochemical cells having an oxidizable active anode material, a cathode current collector, and an electrolytic solution comprising a reducible liquid cathode material and an electrolyte solute dissolved therein.
A particularly effective class of primary electrochemical cells which employs soluble or liquid cathode materials, as opposed to the more conventional solid cathode cells, has undergone rapid development in recent years. In these cells, the active cathode material is usually a fluid solvent for an electrolyte solute which provides conductivity. The active anode of the cell is usually lithium or other highly electropositive metal. During discharge the solvent is electrochemically reduced on a cathode current collector.
One particular type of electrochemical cell of the foregoing class which contains a lithium anode employs a reducible liquid cathode of thionyl chloride. Typically the electrolyte solute dissolved in the thionyl chloride solvent is lithium tetrachloroaluminate. This salt is usually prepared from the Lewis acid aluminum chloride and the Lewis base lithium chloride. A Lewis acid is any compound capable of entering into a chemical reaction by accepting an electron pair to form a covalent bond, and a Lewis base is any compound capable of entering into a chemical reaction by donating an electron pair to form a covalent bond. Lithium/thionyl chloride electrochemical cells have proven to have outstanding weight and volume energy density, long shelf life, and unusually high power density when compared with other cells previously available.